The long-range goal of the proposed project is to explore the responses of the lateral terminal nucleus of the accessory optic system (LTN) and the dorsolateral pontine nucleus (DLPN) in the squirrel monkey in relation to vertical eye movements and eventually to motor learning of the vertical vestibulo ocular reflex (VVOR). To accomplish this goal, three experiments are proposed: (1) The nature of visual information and its flow will be monitored in the LTN and DLPN by extracellular single unit recording to characterize their activity during VVOR and vertical optokinetic nystagmus (VOKN). (2) Once the LTN and DLPN have been characterized we will temporarily inactivate them with muscimol or lidocaine to assess the effects of their inactivation on the normal VVOR and VOKN. (3) The neural pathways conveying visual information to the vertical VOR and vertical OKN cerebellar and brainstem pathways, the LTN and the DLPN, will be anatomically defined in the squirrel monkey. The simplicity of the oculomotor system makes it compelling for study when compared to the complexity of the skeletal motor system. Yet the results of eye movement studies have had a profound impact on understanding the function of motor, sensory, and cognitive systems of vertebrate and human behavior.